Regulation of Constitutive TCR Internalization by the ζ-Chain

Abstract

The ability of a T cell to be activated is critically regulated by the number of TCRs expressed on the plasma membrane. Cell surface TCR expression is influenced by dynamic processes such as synthesis and transport of newly assembled receptors, endocytosis of surface TCR, and recycling to the plasma membrane of internalized receptors. In this study, the internalization of fluorescently labeled anti-TCR Abs was used to analyze constitutive endocytosis of TCRs on T cells, and to investigate the role of the ζ-chain in this process. We found that cell surface TCRs lacking ζ were endocytosed more rapidly than completely assembled receptors, and that reexpression of full-length ζ led to a dose-dependent decrease in the rate of TCR internalization. Rapid TCR internalization was also observed with CD4+CD8+ thymocytes from ζ-deficient mice, whereas TCR internalization on thymocytes from CD3-δ deficient animals was slow, similar to that of wild-type thymocytes. This identifies a specific role for ζ in the regulation of constitutive receptor internalization. Furthermore, chimeric ζ molecules containing non-native intracellular amino acid sequences also led to high levels of TCR expression and reduced TCR cycling. These effects were dependent solely on the length of the intracellular tail, ruling out a role for intracellular ζ-specific interactions with other molecules as a mechanism for regulating TCR internalization. Rather, these findings strongly support a model in which the ζ-chain stabilizes TCR residency on the cell surface, and functions to maintain cell surface receptor expression by sterically blocking internalization sequences in other TCR components.

Imaging T-cell receptor activation reveals accumulation of tyrosine-phosphorylated CD3ζ in the endosomal compartment

“…Accumulation of CD3ζ in the perinuclear vesicles was previously observed for endogenous and GFP-tagged CD3ζ in several Jurkat clones, naïve T cells, and T-cell hybridomas (8,(15)(16)(17)(18) and is consistent with constitutive internalization and recycling of the TcR/CD3 described in various primary cells and cell lines. Indeed, time-lapse microscopy shows that the ZIP reportercontaining vesicles actively move within the cytoplasm and exchange with the plasma membrane (Movie S3).…”

Variation in the Cd3ζ (Cd247) Gene Correlates with Altered T Cell Activation and Is Associated with Autoimmune Diabetes

“…CD3z functions by amplifying the TCR signaling cascade and is necessary for assembly of the TCR/CD3 complex on the surface of T lymphocytes (14,15). It is well established that defective CD3z function leads to impaired activation of T cells upon engagement of the TCR (33,34).…”

“…CD3z is involved in the TCR signaling cascade, and phosphorylation of CD3z at tyrosine residues that are present in ITAMs is one of the earliest detectable events that occurs after TCR engagement (12,13). Moreover, CD3z is important for the expression and assembly of the TCR/CD3 complex on the surface of T lymphocytes (14,15). It was reported that NOD mice have a defect in TCRmediated signaling, and this defect is associated with a block in Ras activation (16)(17)(18).…”

Constitutive and Ligand-Induced TCR Degradation

“…Thus, at steady state a certain amount of TCR is endocytosed, while at the same time an equal amount of TCR is exocytosed. Several studies seem to agree that the constitutive endocytic rate constant for the TCR in resting T cells is ϳ0.01 min Ϫ1 , meaning that 1% of the cell surface-expressed TCR is internalized each minute (11,(15)(16)(17). However, whether the TCR is endocytosed and further processed as an intact receptor or as individual subunits with different endocytic, exocytic, and degradation rate constants remains unclear.…”